1. Field of the Invention
The present invention generally relates to fuses included within semiconductor structures which protect semiconductor devices from excessive voltage and/or current or which selectively and permanently connect/disconnect semiconductor devices from one another.
2. Description of the Related Art
As the size and voltage/current ratings of semiconductor devices becomes smaller, as a result of device miniaturization, the fuses which protect or disconnect such devices must be opened ("blown") with smaller voltages and currents. In an effort to reduce the minimum current/voltage required to open a fuse, conventional fuse structures have a reduced cross-sectional area and have bends in the conductive path to create current crowding. Such structures create a localized high resistance fuse region which causes the fuse to open with smaller voltages and currents.
FIG. 1A illustrates a top view of a conventional current-blow fuse. To reduce the fuse-opening current requirements, conventional fuses make the width of the fuse element (Wf) 10 as small as possible, and make the width of the interconnect conductor (W0) 11 at the end of the fuse as large as possible relative to the length of the fuse element (Lf) 12.
These dimensions result in the fuse resistance being substantially higher than the resistance of the interconnect conductor 11. Furthermore, the step in conductor width (W0 vs. Wf) results in current crowding at the junction of the fuse and the relatively wide interconnect conductor 11. Current crowding also increases the resistance of the fuse and reduces the current required to open the fuse.
This effect is illustrated by the top view of the region 13 where conductive wiring 11 connects to the fusible link 10 in FIG. 1B. Within the region 13 where current crowding occurs, localized heating is increased. This makes it likely that the fuse will open at this point, when it is desired to be blown. The step in conductor width between conductive wiring and the fusible link, improves the consistency of the location at which the fuse will open. This results in a tighter distribution of blow-current compared to fuses having constant width.
Reduction of the fuse-opening current is important because it allows the size of the fuse drivers to be reduced, resulting in a tight fuse pitch, and allows fuses to be opened with lower voltages.